#ks4 physics

Now you see it, now you don't...

Radiation is invisible to the naked eye. Here is a way to observe alpha  radiation (a particle made of two protons and two neutrons) being emitted from a short-range (4-5cm) radioactive source, A cloud chamber can be constructed with a compartment which is packed with some dry ice (solid carbon dioxide) above which an alpha emitting source is mounted. About 2ml of ethanol is soaked onto a ring of felt around the rim of the chamber with a teat pipette. The lid is placed snugly on top and, after a minute or so, vapour trails can be seen shooting out from the radiation source. What's happening? Radiation is being spontaneously emitted and the alpha particles that are ejected ionises the air molecules that they are passing through. This is turn attracts the ethanol vapour (a polar molecule - ask a chemist) that is in the chamber and the dry ice has cooled it sufficiently that the ethanol condenses into the vapour trails we see as we watch the procession of the alpha particles coming away from the source.